Is dense-pack cellulose a good option in the roof slope of a 1960s cape?
I’m doing a lot of work in a town on Long Island, NY (zone 4) that has many cape-style houses. Typically there is poorly installed insulation in the kneewall, kneewall floor and the sloped ceiling above the second floor.
We are proposing:
1. Removing any existing fiberglass batt insulation
2. Installing 1 or 2 inch polyiso board under the roof rafters to create a void.
3. Blocking down at the soffit to eliminate air migration into the roof slope
4. Blocking at the top of the ceiling slope to stop the cellulose and allow us to dense pack
5. Dense packing the void so that the dense pack would extend from the top of the first floor wall to the top of the sloped ceiling on the second floor.
5. The attic above the 2nd floor, when accessible would be air sealed and have loose fill cellulose added.
I like this for a few of reasons:
– The kneewall storage becomes part of the conditioned space. This eliminates the need to air seal or try to insulate the kneewall
– There is a continuour layed of dense-pack cellulose following essentially the entire roof line of the 2nd floor.
– It address the ceiling slope, which would be hard to address another way with out removing sheetrock.
The concerns that have been raised:
– Won’t the cellulose become a huge moldy mess if there is a roof failure.
– it is difficult to create a perfect air seal with cellulose, so could you have a condensation issue against the roof sheathing
– This is not a code compliant structure unless you:
a. put a vapor impermeable insulation of at least R-15 against the roof sheathing. closed cell foam might take care of this at least in the kneewall slope, but would not help where there is already ceiling.
b. leave the underside of the structure with a vaper permeable surface so the structure could dry if it becomes wet.
I’ve been told that my proposal is compliant with the 2009 IEC, but of course no one seems to actually be able to put their hands on one – I guess they don’t want to pay the $109 either.
Any thoughts of comments on this are appreciated.
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